anti-emetics Flashcards
NTs involved in nausea
Histamine, ACh, DA, 5-HT, substance P
Brain regions implicated in nausea and receptors that innervate them
4 main pathways
Chemoreceptor trigger zone (CTZ) stimulates the vomiting centre in the brain. D2, 5-HT3, and NK-1 receptors innervate the CTZ.
An afferent nerve from the GIT contains 5-HT3 and NK-1, and innervates the CTZ
Vestibular nuclei in the inner ear can stimulate nausea through the activation of M and H1 receptors, which is sent to higher centres in the brain, which initiates vomiting.
The higher central can also stimulate vomiting without signalling from the vestibular nuclei
H1 antagonist for nausea mechanism, side effects, uses
Promethazine, for motion sickness, morning sickness, and space motion sickness (NASA uses). Also has antimuscarinic activity.
Drowsiness and sedation side effects
mAChR antagonism for nausea mechanism, side effects, uses
E.g., hyoscine/scopolamine
prophylaxis (preventative) and treating motion sickness.
Has antimuscarinic side effects, e.g., reduced GIT tone, dry mouth, drowsiness.
D2 antagonism for nausea mechanism, side effects, uses
E.g., metoclopramide, domperidone, prochlorperazine.
Antagonism can cause parkinsonism-like symptoms. stimulates gastric emptying.
Used for chemo nausea.
5-HT antagonism for nausea mechanism, side effects, uses
chemo can cause heightened release of 5-HT in the GIT, which can lead to an increase in nausea.
ondansetron blocks 5-HT3 to treat this.
NK-1 antagonism for nausea mechanism, side effects, uses
aprepitant
NK-1 activated by substance P
used in chemo induced nausea (often in combo with ondansetron)
Atypical anti-emetic example, and example of drug used to induce emesis
Steroids such as dexamethasone are used in chemo-induced nausea, but have an unknown mechanism.
Apomorphine is a non-selective DA agonist, and has been used as an emetic in veterinary medicine (but also as a treatment for PD).
